The electrical steel sheets are soft magnetic materials widely used as core materials for transformers, power generators or the like. Especially, grain-oriented electrical steel sheets have good iron loss properties directly leading to reduction of energy loss in transformers, power generators or the like because its crystal orientation is highly concentrated into {110}<001> orientation called Goss orientation. In order to improve the iron loss properties, it is known that reduction of sheet thickness, increase of specific electrical resistance by addition of Si or the like, improvement of orientation in the crystal orientation, application of tension to steel sheet, smoothing of steel sheet surface, refining of secondary recrystallized grains, magnetic domain refining and so on are effective.
Among them, a method of rapid heating during decarburization annealing or a method wherein a primary recrystallization texture is improved by rapid heating just before decarburization annealing is known as the technique for refining the secondary recrystallized grains. For example, Patent Document 1 discloses a technique of obtaining a grain-oriented electrical steel sheet with a low iron loss by rapid heating for a steel sheet rolled to a final thickness to 800˜950° C. at a heating rate of not less than 100° C./s in an atmosphere having an oxygen concentration of not more than 500 ppm before decarburization annealing, and subjecting to decarburization annealing under conditions that a temperature of a preceding zone in the decarburization annealing is 775˜840° C. lower than the temperature reached by the rapid heating and a temperature of subsequent zone is 815˜875° C. higher than the temperature of the preceding zone, and Patent Document 2 discloses a technique of obtaining a grain-oriented electrical steel sheet with a low iron loss by heating a steel sheet rolled to a final thickness to a temperature of not lower than 700° C. at a heating rate of not less than 100° C./s in a non-oxidizing atmosphere having a PH2O/PH2 of not more than 0.2 just before decarburization annealing.
Also, Patent Document 3 discloses a technique of producing an electrical steel sheet having excellent coating properties and magnetic properties wherein a temperature zone of not lower than at least 600° C. in a temperature rising stage of a decarburization annealing step is heated above 800° C. at a temperature rising rate of not less than 95° C./s and an atmosphere of this temperature zone is constituted with an inert gas containing an oxygen of 10−6˜10−1 as a volume fraction, and an atmosphere in a soaking of the decarburization annealing is H2 and H2O or H2, H2O and an inert gas as a constituent and has PH2O/PH2 of 0.05˜0.75 and a flow amount per unit area of 0.01˜1 Nm3/min·m2, and a deviation angle of a crystal orientation of crystal grains of the steel sheet in a mixed region between coating and steel sheet is controlled to an adequate range from Goss orientation, and Patent Document 4 discloses a technique of producing a grain-oriented electrical steel sheet having excellent coating properties and magnetic properties wherein a temperature zone of not lower than at least 650° C. in a temperature rising stage of a decarburization annealing step is heated above 800° C. at a temperature rising rate of not less than 100° C./s and an atmosphere of this temperature zone is an inert gas containing an oxygen of 10−6˜10−2 as a volume fraction, while an atmosphere in a soaking of the decarburization annealing is H2 and H2O or H2 and H2O and an inert gas as a constituent and has PH2O/PH2 of 0.15˜0.65, whereby a discharge time indicating a peak of Al emission intensity in GDS analysis of a coating and a discharge time indicating that of Fe emission intensity is ½ of a bulk value are controlled to adequate ranges.